So-called side curtain airbags are known in vehicle technology. These airbags are located in the area of the side roof rail of a motor vehicle and expand in front of the side windows and possibly the B-pillar of a motor vehicle in case of need. Such a curtain airbag by its nature exhibits a relatively large basic area. This large area results in the problem of evenly discharging the gas emerging form a single gas generator into the airbag.
A curtain airbag unit exhibits a large-surface airbag skin and a gas generator for filling of the airbag skin. The airbag skin typically has an upper edge, which is fixed in the area of the roof rail of the motor vehicle, so that the longitudinal direction of the airbag extends along the longitudinal axis of the vehicle. Filing preferably occurs from the upper edge. Two concepts are currently used for this result.
In the first concept, the gas generator is located on one of the two ends of the upper edge (generally the rear end), and a long, thin metal lance forming several outlet openings extends from the gas generator into the inside of the airbag skin, said metal lance distributes the gas over the length of the airbag skin.
In a second concept, the airbag skin exhibits an accommodation area for the gas generator in the area of the upper edge between the front and the rear end, which extends into the inside of the airbag skin or which is at least connected with the inside. For this purpose the accommodation area can be L-shaped, for example.
If, according to the first concept, gas guide elements in the form of metal tubes are used, at least two disadvantages result: on the one hand such tubes are relatively thin in relation to their length, which makes them very susceptible to damage and therefore there are considerable transport costs involved during transport from the manufacturer to the site of final assembly. Furthermore, the assembly unit of gas generator and gas guide element is not thrust neutral and therefore constitutes a risk.
Therefore, the suggestion has already been made to manufacture gas guide elements of fabric. A gas guide element made of fabric is described, for example in JP 2002-187519 A.
One problem in the use of tubular gas guide elements made of fabric is that if cylindrical gas generators which are thrust neutral are used, the hot gas first strikes directly against the inner walls of the fabric tube. This can lead to failure of the material and therefore to faulty function of the airbag.
In the second concept, the following problem occurs: generally, cylindrical gas generators are used which are formed so as to be thrust neutral for reasons of safety. This means that the gas outlet openings are arranged so as to be rotationally symmetrical on a part of the jacket surface of the gas generator. Without additional measures there would be the problem that airbag fabric would be directly subjected to the stream of the hot gases and would possibly be damaged. Therefore deflectors are used which protect the airbag fabric against the outflowing gas.
Such a deflector, implemented in the form of a U-shaped metal sheet, is known from patent WO 02/079008 A1. Furthermore, a gas guide element made of fabric which is sewn into the airbag skin is known from this publication.
A disadvantage of such a deflector element is that the airbag unit, when finally assembled and complete, does not behave in a manner which is thrust neutral. Namely, if the airbag becomes overheated due to a thrust imbalance, the airbag skin consisting of plastic fabric material may become burned.